To istall a Gen3/4 LS engine into a early mustang we offer a weld-in kit. This is our complete street rod kit.
You can view these mounts HERE.
The frame side of the mounts will need to be welded to the factory cross member like shown.
You will install the engine side of the motor mounts reverse. The "D" will go on the passenger' side, the "P" will go on the drivers' side. This customer used a 2004-2006 GTO front sump oil pan. There are several companies making aftermarket front sump LS oil pans.
This example is using an LS Vortec truck spacing balancer and our billet alternator/power steering bracket DD-LS-ALT-PS.